1. Field of the Invention
The present invention relates to a dielectric ceramic utilizable for a high frequency region such as the microwave region and the millimeter wave region, as well as a dielectric resonator, a dielectric filter, a dielectric duplexer and a communication unit using the ceramic.
2. Description of the Related Art
Dielectric ceramics are widely used as materials for a dielectric resonator, a dielectric filter and a circuit board mounted on an electronic devices which are utilized in high frequency regions such as the microwave region and the millimeter wave region for various applications including portable telephones, personal wireless sets and satellite broadcast receivers, for example.
As the dielectric characteristics required for such a dielectric ceramic for high frequency, enumerated are: (1) a large specific dielectric coefficient (∈r) for meeting the requirement of miniaturization since the wavelength of an electromagnetic wave is shortened by 1/(∈r)xc2xd in a dielectric; (2) a small dielectric loss, that is, a large Q value; (3) excellent temperature stability of resonant frequency, that is, the temperature coefficient (xcfx84f) of resonant frequency being in the vicinity of 0 (ppm/xc2x0 C.), etc.
Conventionally, dielectric ceramics represented by such as a Ba(Zn,Ta)O3-type composition, (Japanese Examined Patent Application Publication No. 58-25068), a Ba(Sn,Mg,Ta)O3-type composition (Japanese Examined Patent Application Publication No. 3-34164), a (Zr,Sn)TiO4-type composition (Japanese Examined Patent Application Publication No. 4-59267), and a Ba2Ti9O20 composition (Japanese Unexamined Patent Application Publication No. 61-10806), are known.
However, while the Ba(Zn,Ta)O3-type and Ba(Sn,Mg,Ta)O3-type materials have very large Q values (at 1 GHz) ranging from 150,000 to 300,000, the specific dielectric constants (∈r) are relatively small, ranging from 24 to 30.
On the other hand, the (Zr,Sn)TiO4-type and Ba2Ti9O20-type materials have relatively large specific dielectric constants (∈r) of from 37 to 40, and large Q values (at 1 GHz) of from 50,000 to 60,000. However, it is difficult to realize a larger specific dielectric constant (∈r), for example, to realize a value over 40.
In recent years, the requirements of reduction in loss and miniaturization for electronic devices have been increased. Accordingly, requirements for developing dielectric materials which have further excellent dielectric characteristics, especially both a large specific dielectric constant (∈r) and a large Q value, have been increased. However, the present technologies cannot meet these requirements fully.
Hereupon, one of the objects of the present invention is to provide a dielectric ceramic for high frequency which has a large specific dielectric constant (∈r) of from 40 to 60, a large Q value (at 1 GHz) of about 25,000 or more, and a temperature coefficient (xcfx84f) of resonant frequency which can be controlled within the range of about 0xc2x130 (ppm/xc2x0 C.). Another object is to provide a dielectric resonator, a dielectric filter, a dielectric duplexer and a communication unit using the ceramic.
To achieve the above-described objects, a dielectric ceramic for high frequency according to the present invention is characterized by comprising Ca, Ti, Mg, Zn, Nb and Al, by having a constitution represented by the formula:
yCaTiaO1+2axe2x88x92(1xe2x88x92y)xCa{(MgzZn1xe2x88x92z)⅓Nb⅔}bO1+2bxe2x88x92(1xe2x88x92y)(1xe2x88x92x)Ca(Alxc2xdNbxc2xd)cO1+2c (where x and y are each a molar ratio), wherein xcex1, x, y, z, a, b and c are in the ranges of the following formulae xcex1=(1xe2x88x92y)x: xcex1xe2x89xa60.340; 0 less than xxe2x89xa60.600; 0.380xe2x89xa6yxe2x89xa60.570; 0xe2x89xa6zxe2x89xa61.000; 0.980xe2x89xa6axe2x89xa61.050; 0.980xe2x89xa6bxe2x89xa61.050; and 0.980xe2x89xa6cxe2x89xa61.050, and by comprising a perovskite crystal phase as a main crystal.
Another dielectric ceramic for high frequency according to the present invention is characterized in that it is obtained by further including Ta in the above-described dielectric ceramic for high frequency, and it has a constitution represented by the formula: yCaTiaO1+2axe2x88x92(1xe2x88x92y)xCa{(MgzZn1xe2x88x92z)⅓(NbdTa1xe2x88x92d)⅔}bO1+2bxe2x88x92(1xe2x88x92y)(1xe2x88x92x)Ca{Alxc2xd(NbdTa1xe2x88x92d)xc2xd}cO1+2c (where x and y are each a molar ratio), wherein xcex1, x, y, z, a, b, c and d are in the ranges of the following formulae xcex1=(1xe2x88x92y)x: xcex1xe2x89xa60.340; 0 less than xxe2x89xa60.600; 0.380xe2x89xa6yxe2x89xa60.570; 0xe2x89xa6zxe2x89xa61.000; 0.980xe2x89xa6axe2x89xa61.050; 0.980xe2x89xa6bxe2x89xa61.050; 0.980xe2x89xa6cxe2x89xa61.050; and 0 less than d less than 1.000.
In each above-described dielectric ceramic for high frequency, the symbols a and b are preferably within the following ranges: 1.000xe2x89xa6axe2x89xa61.050; and 0.980xe2x89xa6bxe2x89xa61.000.
Furthermore, a dielectric resonator according to the present invention is characterized by having a dielectric ceramic actuated by electromagnetic coupling with the input/output terminals, wherein the dielectric ceramic is composed of the above-described dielectric ceramic for high frequency.
Furthermore, a dielectric filter according to the present invention is characterized in that it comprises an outer coupling as well as the above-described dielectric resonator.
Furthermore, a dielectric duplexer according to the present invention is characterized by comprising at least two dielectric filters, input/output connection connected to each of the dielectric filters, and an antenna connection connected commonly to the dielectric filters, wherein at least one of the above-described dielectric filters is the dielectric filter described above in the previous paragraph.
Furthermore, a communication unit according to the present invention is characterized by comprising the above-described dielectric duplexer, a transmission circuit connected to at least one of the input/output connections of the dielectric duplexer, a receiving circuit connected to at least one of the input/output connection which is different from the above-described input/output connection connected to the transmission circuit, and an antenna connected to the antenna connection of the dielectric duplexer.